Chelsea forward Diego Costa appears to bite Gareth Barry after earlier gesturing at fans as he left the field at half time during the Blues' FA Cup tie against Everton at Goodison Park

The Colombian striker was one of a number of European stars to be tempted by the Chinese Super League and in February completed a £33.1million switch to Guangzhou Evergrande.

It weakened an already struggling attacking group, who before a recent glut of nine goals in three games had only managed 36 goals in 26 La Liga fixtures.

And while Antoine Griezmann has 16 league strikes to his name, the next best is Fernando Torres with only five, meaning the Madrid outfit have the desire and the funds to bring in a forward over the summer.

Lukaku's power and direct attacking means he is seen as the ideal replacement for Martinez and he could be the perfect foil for Griezmann.

However, United have reportedly been after the 22-year-old forward since last summer and are said to retain their desire to sign a striker this summer.

Louis van Gaal's failure to buy an attacking player in January has been exploited by an injury crisis at Old Trafford and the Red Devils are said to be desperate not to make the same mistake again.

And they are not the only Premier League club, as The Sun reported that Chelsea are interested in re-signing Lukaku despite having sold him to Everton just two years ago.

The Blues will stop at nothing to sign him either, with technical director Michael Emenalo said to be ready to spend £56m on the player.